Fine lithographic processing using a photoresist has been performed in the production of semiconductor devices. In the fine processing, a thin film of a photoresist is formed on a semiconductor substrate such as a silicon wafer, this film is irradiated with an active light radiation such as UV radiation through a mask pattern provided with the pattern of a semiconductor device, the film is developed, and the substrate is etched using the obtained photoresist pattern as a protective film, thereby forming fine protrusions and depressions corresponding to the pattern on the substrate surface. However, a trend has recently been developed to the increase in the degree of integration of semiconductor devices and a transition to a shorter wavelength of the active light radiation used, namely, from KrF excimer lasers (248 nm) to ArF excimer lasers (193 nm). As a result, an effect on reflection of active light radiation from semiconductor substrates has been becoming a serious problem.
Further, films including a metal element such as silicon or titanium and known as hard masks have been used as underlayer films between the semiconductor substrate and the photoresist (see, for example, Patent Document 1). In this case, since the resist and the hard mask differ significantly in constituent components from each other, the removal rate thereof by dry etching strongly depends on the type of gas used for dry etching. Further, by selecting the adequate gas, it is possible to remove the hard mask by dry etching, without a significant reduction in the photoresist film thickness. Thus, in recent years, resist underlayer films have been disposed between semiconductor substrates and photoresists in the production of semiconductor devices to attain a variety of effects such as an anti-reflection effect. Compositions for the resist underlayer films have also been investigated, but due to a great variety of the required characteristics thereof, the development of new materials for the resist underlayer films is desired.
For example, the application, to the lithography process, of a polysiloxane material obtained from a silane having a diester structure including an acid unstable group has been described (see Patent Document 2).